pgsql: Reject degenerate SPLIT PARTITION with DEFAULT partition

Reject degenerate SPLIT PARTITION with DEFAULT partition

ALTER TABLE ... SPLIT PARTITION allows a DEFAULT partition to be created
as one of the replacement partitions when the parent table does not
already have one. However, it should not allow the degenerate case where
a non-DEFAULT partition keeps exactly the same bound as the split
partition and the command merely adds a DEFAULT partition through the
SPLIT PARTITION path.

Detect that case by comparing the bound of the split partition with the
bound of the only non-DEFAULT replacement partition, and raise an error
when they are the same. Users should add a DEFAULT partition directly
with CREATE TABLE ... PARTITION OF ... DEFAULT or ALTER TABLE ... ATTACH
PARTITION ... DEFAULT instead.

Author: Chao Li <lic(at)highgo(dot)com>
Reviewed-by: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Discussion: https://postgr.es/m/C18878AB-DEB2-4A61-9995-A035DD644B81@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d8af73010033cb8ad6c941942d6b03d74d7e4f7e

Modified Files
--------------
src/backend/partitioning/partbounds.c | 150 ++++++++++++++++++++++++++
src/test/regress/expected/partition_split.out | 59 ++++++++++
src/test/regress/sql/partition_split.sql | 52 +++++++++
3 files changed, 261 insertions(+)